Generally, in a wind power generation system with a permanent magnet generator or an induction generator, a wind power is transmitted by using a transmission mechanism to transmit a rotational power to a generator. A rotation speed and a torque of the generator are determined according to the magnitude of the wind power. Therefore, the rotation speed thereof is required to be limited for ensuring that the rotation speed varies in a specific range. When the wind power is higher or lower than a standard range, the generator is turned off until the wind power is in the standard range. In this passive power generation system, an AC-to-DC converter and a DC-to-AC converter are required to output the wind power. However, this converting method will result in a power loss of the power conversion, hence deteriorating a power conversion efficiency and increasing the cost of the generation equipment.
Besides, in the induction wind generator, when the inputted power is altered, or when the load of the utility grid is raised, the induction generator cannot control the excitation current thereof. Thus, when the power required for a load terminal is increased, a voltage from an output terminal of the generator cannot be constant, resulting in a reduction of an output power quality.